Here's a site that tells all about growing clematis from seed: Clematis from seed.
Note that unless your clematis is a species clematis it is a hybrid and seed from it will not produce the same flower. It is an interesting thing to try if you have the time and the patience to follow through. There have been several discussions on the forum recently about it.

I have Belle of Woking and what is supposed to be Ramona but is very purple and only have 5 petals per flower. Do these plants give off seeds for replanting?

"Ripe' seeds must be dark brown and will fall away easily from the pod. They are the 'big and fat' dark seeds and some will have feather like tails on them. If you collect seeds too soon they will not germinate.
Here are a few pictures of some 'ripe' seedheads which are ready to be collected. Notice that the seeds have turned completely brown. Wait until they look dry and fall easily off the pod:
Here's a group 2, large flowered hybrid seedhead with feathery tails. The seed is turning dark and is ready to collect:
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and here is a Viticella type seed head almost ready to collect. I will let it dry a bit more before collecting:
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and here is some still green, 'un-ripe' seed forming:
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Suzy

I'm just learning all of this also. It's very interesting. Great photos Suzy. I had that same question. So that's what they look like. There's Brian's webpage again. Cool! It's good.

Thanks for the great pictures. I have tried to gather seeds and grow for a few seasons and I just discovered some ripe seeds and now realize that the seeds that I was planting were never pollinated so they never grew into that heart shaped seed. I have only five or six seeds that are big and heart shaped on a plant with maybe 15 clusters of seeds that were not pollinated. What can we do to help the plant set seed, possiblly rub the flowers together to insure polLination? Thanks- cindy

I have been wondering this very same thing.....

Suzy, are you saying that the "seed" in your third picture will eventually get the the point of the "seed" in the first picture? Or will the "seed" in the third picture simply dry as is?

Sandy, the two seeds in the third picture are fertilized seed that still have to finish maturing. When they do, they will appear brown like the ones in the second picture.

Sandy, different clematis have different looking seedheads. Some are feathery, some are not. The seed in the third picture (from a 'Betty Corning') will stay the same, but will turn darker when they are 'ripe'. The seed must be ready to fall off the vine naturally to be ripened. By this, I mean that it will fall off easily when only a gentle 'nudge' is given.
Suzy

Cindy, yes, you can 'hand' pollinate your flowers if you do it at the right stages. I gently rub the flowers together. The mother plant must be ready to accept pollen and the father flower must have some pollen, the more the better. If you are unsure about when is the right time for both, just try to pollinate every few days and some will be successful. You may get some interesting hybrids by using several different clematis !
Suzy

I'm glad you asked this question, cmpman1974 :-)

Now that suzymac supplied great pictures so I know what I'm looking for, I have a couple more questions:

1. I have one Clematis that is in the Spring flowering category. I think it usually will bloom again just before fall, though not as abundant. If I cut all the seed heads but one or two, will that still provide me with seeds and blooms late fall?

2.And, if I just leave all of the heads on there now, when do they usually mature-- aka, do I have to let them stay on for the whole summer looking so sparse?

I just got on here just to see what the seeds actually looked like because I had never seen any before and have always seen people offering seeds. Well I realize that I do have seeds on my Clematis but when I picked them I realized that they are still green if I let them dry will they still germinate for me? And as looking on that web page about growing Clematis from seed do I understand right that you need to let these seeds sit out over winter to get the freeze-thaw action before they will germinate.
I also have a Clematis and have forgotten the name I have had it for a long long time years. If I figure out how to post a pix of it on here maybe someone could tell me what kind it is it is maybe 20 or more years old.
Thanks Jan

I've been gifted with some seeds from a multi-blue clematis. How do I plant this seed pod? Can I wintersow it or is it better to start it in a pot? When should it be sown?

I'm too impatient to grow clematis from seed but here's a page that tells you all about it.